Preheat oven to 350°F (180°C).
In a bowl mash ½ ripe banana, then combine with peanut butter and maple syrup. Stir until smooth.
Add protein powder, oat flour, cocoa powder, baking powder and a pinch of salt.
Start mixing with a fork, then use your hands to knead the dough until smooth. If too thick, add 1 to 2 teaspoons of nondairy milk and keep kneading until smooth.
Divide the dough into 2 parts, then roll each into round discs about 0.2 inches (0.50 cm) thick.
Add a teaspoon of peanut butter into the center of one disc, then cover with the second piece of dough. Gently press down edges to seal the cookie.
Place over a parchment paper covered baking sheet and bake in hot oven for 10 to 12 minutes. Let cool for at least 10 minutes before serving.